First, prepare the avocado mash.
In a small bowl, mash the avocado with a fork until it's nearly smooth.
Stir in the lime juice and minced garlic. Press a piece of plastic wrap directly onto the surface of the mixture to prevent browning and chill in the refrigerator.
Next, create the spice rub.
In another small bowl, combine the cumin, oregano, salt, and black pepper. Lightly coat the portobello mushrooms, sweet pepper halves, and red onion slices with nonstick cooking spray, then sprinkle the spice rub evenly over all sides of the vegetables.
Preheat your grill to medium heat.
Place the seasoned vegetables directly on the grill rack.
Grill until crisp-tender, turning once. The peppers will take about 8-10 minutes, the mushrooms 10-15 minutes, and the onions 15-20 minutes.
Remove each vegetable from the grill as it finishes cooking.
Once the vegetables are off the grill, place the tortillas on the rack for 20-40 seconds per side, just until they are warm and have light grill marks.
Remove them and wrap in a clean towel to keep warm. Thinly slice the grilled mushrooms and sweet peppers, and coarsely chop the onion.
Time to assemble!
Spread a generous layer of the chilled avocado mixture onto each warm tortilla.
Top with the sliced grilled vegetables, fold, and serve immediately. Offer extra lime wedges on the side for a fresh squeeze of citrus.
Don't overcrowd the grill.
Cook the vegetables in batches if necessary to ensure they get a beautiful char instead of steaming.
