Cut eggplant crosswise into rounds a little less than 1/2-inch thick.
Cut zucchini lengthwise into three strips each.
Cut onion into slices about 1/2-inch thick.
Spread eggplant, zucchini, onion, portobellos, and bell peppers on a work surface. Brush lightly with oil and season with salt and pepper.
Preheat grill until very hot. Grill vegetables about 2-3 minutes per side. Using tongs, remove tender pieces and keep warm in a covered bowl while any remaining pieces grill.
Cut all vegetables into thin, bite-size strips.
Whisk together miso, lemon zest, lemon juice, amino acids, agave nectar; flaxseed oil, garlic, and Sriracha sauce (if using) until emulsified.
Add sliced vegetables and serve.