Preheat your oven to 425°F (220°C). Line a large sheet pan with parchment paper for easy cleanup.

In a small bowl, combine all the fajita seasoning ingredients: chili powder, cumin, smoked paprika, garlic powder, onion powder, cayenne (if using), salt, and black pepper. Set aside.

Add the sliced bell peppers and red onion to the prepared sheet pan. Drizzle with 2 tablespoons of avocado oil and sprinkle with half of the fajita seasoning. Toss to coat evenly and spread in a single layer.

Roast the peppers and onions for 8 minutes until they begin to soften and char slightly around the edges.

While vegetables roast, pat the shrimp dry with paper towels. Place in a bowl and toss with remaining 1 tablespoon of avocado oil, minced garlic, and the remaining fajita seasoning until evenly coated.

Remove the pan from the oven. Push the vegetables to one side and add the seasoned shrimp in a single layer on the other side of the pan.

Return the pan to the oven and roast for an additional 4-5 minutes, or until the shrimp are pink, opaque, and slightly charred. The shrimp should curl into a C-shape when done.

Remove from oven and squeeze fresh lime juice over everything. Serve immediately in warm tortillas with sliced avocado, fresh cilantro, and a dollop of sour cream or Greek yogurt if desired.