Place the top rack of your oven about 6-7 inches from the broiler, and turn broiler on to HIGH.
Place the thawed hash browns in a microwave safe bowl. Toss with salt and pepper to taste. Cover tightly and cook in the microwave on high for 6-8 minutes--until heated through--removing from the microwave to stir about halfway through.
While the hash browns are cooking, sauté the onion and garlic with 2 tablespoons of water, in a large, broiler-proof skillet, on medium high heat, until browned and fragrant, about 5 minutes. Add more water little at a time if things begin to stick.
Add the thawed mixed vegetables, lentils, and thyme to the pan, reduce to medium heat, and stir to heat through, about 2-3 minutes.
Make a 'slurry'. When the potatoes are finished cooking, add one cup of the hash browns to a blender with 1 cup of plant milk, and blend on high for 10 seconds. DO NOT OVERBLEND or the mixture will become paste-like. The slurry should be just thin enough to pour out of the blender.
Add the slurry to the pan with the hot vegetable and lentil mixture, and stir gently until combined. DON'T HEAT MORE THAN A MINUTE or the slurry will get too thick. Remove the skillet from the heat, and use a spoon and or your hands to spread the remaining hash brown potatoes over the top in an even layer.
Place the skillet in the oven, and broil on HIGH for 8-10 minutes or until the hash browns reach the desired crispness. Check after about 5 minutes or so tome sure the topping isn't burning. IF IT'S GETTING TOO DARK, lower the rack in theooven OR the broiler temperature to LOW if it's getting done too fast, or cover with foil.
Notes
To Save Time.
To make this recipe in 20 minutes, you'll need to multi-task! The hash browns will be cooking in the microwave, while the onion and garlic are satueeing, etc.
You can make this EVEN FASTER if you skip the fresh onion, garlic and thyme and substitute 2-3 teaspoons onion powder, ¼ teaspoon garlic powder and 3 teaspoons dried thyme. But I recommend using fresh for the very best result.
Hash Browns/Potatoes.
Look for organic hash browns with no added ingredients noted on the label.
It's best to thaw them overnight in the fridge. You can also thaw them under warm running water in a colander; just be sure to gently squeeze out the excess liquid.
You can substitute sweet potato hash browns, or for a more traditional recipe, use instant mashed potatoes like Bob's Red Mill or left over mashed potatoes. I have not tested using mashed potatoes yet. When you mix potatoes and plant milk for the slurry, you want it to be thick, but still thin enough to pour out of the blender. I believe about 2 inches of potato topping will give you a good result with this recipe. (I'll update once I've thoroughly tested.)
Mixed Vegetables.
I used a blend of peas, carrots, green beans and corn, but any combination of small-diced mixed vegetables will work.
It's best to thaw them overnight in the fridge. You can also thaw them under cold water in a colander; just be sure to gently squeeze out the excess liquid.
Lentils.
This recipe works well with firm lentils. I used black, but brown or green would also work.
Look for low sodium lentils, and make sure to drain and rinse well. This will remove much of the sodium in canned lentils.
You can also used pre-cooked lentils from stores like Trader Joe's, or leftover cooked lentils.
If you don't have a broiler proof skillet...
You can start the recipe in a regular skillet, and then transfer the vegetable and lentil mixture to a broiler proof casserole dish before topping with hash brown potatoes. In this case, you'll need to increase the cooking time, because the baking dish will not as hot as the skillet would be. I recommend cooking on LOW BROIL and increasing the cooking time by 5-10 minutes, or until hot all the way through.
See the post (above) for a helpful list of suggested variations and substitutions.