Heat the grill to high, lightly oil the grates.
In separate piles, arrange the zucchini, mushrooms and scallions on a baking sheet. Drizzle with 2 tablespoons of oil; season with salt and pepper.
Working in batches if necessary, remove each pile of vegetables from the baking sheet. Grill, turning once, until lightly browned and tender: 2 minutes for scallions, 6 minutes for mushrooms, 8 minutes for zucchini.
Return all vegetables to the baking sheet. Slice the mushrooms into 1/2 inch wide strips and set aside.
Brush tortillas with 1 tablespoon of oil; grill, turn frequently until browned and very crispy, about 2 minutes. Place 1 tortilla on each serving plate; cover evenly with mushrooms and zucchini. Using Kitchen sheers, snip scallions over the vegetables.
Top with salsa, and optional to sprinkle with feta.