Preheat oven to 400 F. Line a sheet pan with parchment.
Pierce squash and microwave for 5 min. Slice spaghetti squash in half lengthwise and scoop out seeds. Rub inside of squash with 1 Tbspolive oil and sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper.
Place squash cut-side down and roast for 40 minutes until squash can be easily pierced with a knife.
When squash is cool enough to handle, use a fork to remove flesh. Reserve shells.
Heat 1 Tbsp olive oil in a large skillet over medium heat. Add onions and sauté for 3-4 minutes until they start to soften and turn translucent. Add peppers and continue sautéing for 3 minutes.
Stir in black beans, corn, cumin, chili powder, paprika, onion powder, garlic powder, remaining salt and pepper. Let mixture warm for a couple minutes.
Fold in spaghetti squash and cilantro.
Serve stuffed in squash shells with diced avocado and additional cilantro.