Heat 10-inch nonstick skillet over medium-high heat until hot, about 2 minutes. Add corn and cook, stirring occasionally, until kernels begin to brown and pop, 3 to 5 minutes; transfer corn to medium bowl.
Heat 2 tablespoons vegetable oil in the now-empty skillet over medium heat until shimmering; add onion and cook, stirring occasionally, until softened, about 3 minutes. Add garlic and chili powder and cook until fragrant, about 1 minute; stir in beans and cook until heated through, about 1 minute. Return corn to skillet and toss to combine; gently press mixture with spatula to lightly crush black beans.
Transfer mixture a medium bowl, stir in jalapeños and lime juice.
Preheat the oven to 425 degrees and spray a baking sheet with cooking spray.
Warm tortillas according to package directions until soft and pliable. Spoon 2 tablespoons of filling and 1 tablespoon of cheese onto the lower third of each tortilla and roll tightly. Place seam side-down on the prepared baking sheet. Repeat with remaining tortillas.
Use remaining tablespoon of vegetable oil to brush the tops of the taquitos lightly, and sprinkle with kosher salt. Bake 14-17 minutes, or until the tortillas are crisp and golden-brown. Serve with salsa, sour cream, and guacamole.