Preheat oven to 425ºF and grease a baking sheet with nonstick spray. Combine potatoes, garlic, olive oil, cumin, chile powder, salt, and pepper in a large bowl and toss to evenly combine. Spread onto a prepared baking sheet in a single, even layer. Roast for approximately 25 minutes, until potatoes are golden-brown and fork-tender.
During the last 10-15 minutes of roasting potatoes, warm a small skillet with 1 1/2 teaspoons olive oil over medium heat. Add onions, season will salt and pepper to taste, and sauté until translucent, about 5 minutes. Turn off heat.
Warm a large skillet with 1 tablespoon olive oil over medium-low heat. Crack eggs into pan, season with salt and pepper, and cook 4-6 minutes, or until whites are set and yolks are cooked as desired.
Meanwhile, toast tortillas in a skillet set over medium to medium-low heat, or directly on a gas grill, for 1 1/2 - 2 minutes per side, or until golden-brown and crisp.
Spread a thin layer of sour cream over each tortilla. Top with potatoes, onion, fried egg, and avocado slices. Serve immediately.