Press the tofu for at least 20 minutes. Press the tofu by slicing each block of tofu in half (creating two thinner slabs) and lining paper towels under, in between and on top of the stacked slabs to absorb water from the tofu. I recommend putting a cutting board on top of the tofu blocks and weighing it down with something heavy. This works, or you can invest in a tofu press (my preferred method).
Prepare the vegetables as described in the ingredients list.
Prepare the marinade by combining the tamari, ½ cup of water, garlic, ginger, maple syrup, rice vinegar and sriracha into a small sauce pan. Bring to a simmer.
Add the cornstarch and 1 tbsp of water in a separate bowl and whisk to combine until all lumps are removed.
Add the cornstarch slurry to the simmering marinade and continue to simmer, stirring frequently, until the marinade has thickened. About 6-8 minutes. Transfer the marinade to a dish large enough to hold the skewers while marinating.
Slice the pressed tofu into 1-inch cubes.
Thread the skewers with your desired ingredients (this is the fun in shish kebabs! They can be make-your-own) and lay each skewer into the marinade. Cover and let the skewers rest in the refrigerator for at least one hour).
Preheat your oven (to 400º) or grill (I like a hot grill).
If grilling, lay the skewers out on a hot grill. Grill for ~10 minutes, then turn each skewer and baste with additional marinade. Grill for another ~5 minutes until the vegetables begin to char slightly. Remove the skewers from the grill and serve immediately.
If roasting, add the skewers to a baking sheet and roast on the middle rack for about 15 minutes. Pause to turn the skewers and baste with the marinade. After 15 minutes, switch to the broiler and allow the vegetables to char under the broiler. Keep an eye on them, as they will burn quickly. About 2-4 minutes. Remove the skewers from the oven and serve immediately.