If using wooden skewers, cover them in water and let them soak for at least 20 minutes (so they don't burn).
Cut the tofu into 1-inch thick slices, and press for at least 15 minutes. (See notes.)
Whisk together all of the marinade/dipping sauce ingredients and set aside.
Cut the squash, pineapple and eggplant, and divide the pieces into 8 equal piles. Cut the tofu and add the pieces to the piles. (See notes)
Place the squash, pineapple and eggplant and tofu on the skewers, alternating as you go. (You may have to push hard to get the skewer through the squash. SEE NOTES for tips to assemle your kebabs.)
Lay the assembled kebabs on a cutting board or baking sheet, and brush with some of the marinade. Be sure to leave about 3/4 of the sauce for dipping.
Grill on medium-high, or broil on high on a baking sheet or broiler pan, for about 5-7 minutes per side, or until the squash is tender. Turn the kebabs halfway through cooking, BUT keep an eye on the eggplant so that it doesn’t burn. Flip more often if anything is getting too dark.
To reduce fat: Reduce the peanut butter to 1/4 cup--or leave it out completely. Since the sauce will be thinner, you won't use as much. But if desired, you can increase the other ingredients a little to make more sauce. (There's a 'servings' adjuster at the top of the recipe; for example, you can increase from 8 servings to 12 to increase the sauce volume by 50%.) Also, I did not use oil, and my skewers did not stick. But if you're not using peanut butter, you may want to use a non stick surface or very lightly oil your grill.
For nut free: Substitute tahini or seed butter for the peanut butter.
To keep it healthy: leave the skins on the eggplant--that's where the antioxidants are.
To speed things up: Skip the skewers and toss the pieces with the sauce in a plastic bag, then grill in a grill basket or broil on a broiler or sheet pan.
To spice things up: This is not a very spicy recipe, but if you like a bit more heat, add a pinch of cayenne or crushed red pepper flakes to the peanut sauce.
Tips for making kebabs: Divide up your pieces: I've given exact numbers for the tofu/veggie pieces here (24, because I used large skewers), but really, when making a kebabs recipe like this one, don't worry too much about the ingredient portions. Just everything into 1-inch pieces, dividing each ingredient into 8 separate piles (or the number of skewers you have) as you go. At the end, you should have relatively equal piles will all of the ingredients, and you can then just alternate them on the skewers. Leftover ingredients: I had some leftover squash, pineapple and eggplant pieces after making my kebabs. I just tossed them into a 1 qt. bag and labelled it 'Thai veggies.' Some weeknight I'll toss those into a pot with a Thai sauce for an easy dinner.
To press tofu: Cut the block into 1 inch slices, wrap in clean kitchen towels or paper towels, and place a heave object on top. I like to use my biggest Dutch oven.