Preheat your grill to medium-high heat (around 400°F).
Toss the prepared vegetables with olive oil, chili powder, cumin, salt, and pepper in a large bowl.
Place the vegetables on the grill and cook for 4-5 minutes per side, or until they have nice grill marks and are tender but still slightly crisp.
While the vegetables are grilling, prepare the guacamole. Mash the avocados in a bowl, then mix in lime juice, diced onion, tomatoes, cilantro, and jalapeño if using. Season with salt to taste.
Warm the tortillas on the grill for about 30 seconds per side.
Slice the grilled vegetables into strips.
Assemble the tacos by spreading guacamole on each tortilla and topping with the grilled vegetables.
Garnish with extra cilantro and serve with lime wedges.