Preheat your grill to medium-high heat (around 400°F).
Toss the sliced vegetables with olive oil, garlic powder, salt, and pepper in a large bowl.
Grill the vegetables for 4-5 minutes per side until they have nice grill marks and are tender but still slightly crisp.
While the vegetables are grilling, prepare the guacamole by mashing the avocados in a bowl and mixing in the lime juice, diced onion, tomato, cilantro, and salt.
Warm the tortillas on the grill for about 30 seconds per side.
Spread a generous layer of guacamole on each tortilla.
Layer with fresh spinach and the grilled vegetables.
Roll up tightly, tucking in the sides as you go.