Cut avocados in half, remove pits, and scoop flesh into mixing bowl. Mash with fork or potato masher until mostly smooth.
Add minced garlic, sea salt, black pepper, lime juice, cumin, and crushed red pepper to mashed avocado. Stir until well combined.
Fold in chopped cilantro, black beans, corn, and diced red onion. Mix gently until evenly distributed. Taste and adjust seasoning if needed.
Heat non-stick skillet over medium heat and add 1 tablespoon olive oil.
Lay out tortillas and divide avocado mixture between them, spreading on one half of each tortilla. Leave small border around edges. Do not overfill.
Fold each tortilla in half to create half-moon shape. Press down gently so filling spreads without squishing out sides.
Place folded quesadilla in hot skillet. Cook for 2 to 3 minutes on first side until golden brown and crispy.
Use wide spatula to carefully flip quesadilla. Press down gently with spatula. Cook for another 2 to 3 minutes on second side until golden and crispy.
Remove to cutting board and repeat with remaining tortilla. Let rest for 1 minute before slicing.
Slice each quesadilla into 3 to 4 wedges. Serve immediately while hot and crispy.