Heat 1/2 tablespoon avocado oil or olive oil in a large skillet over medium-high heat.
Add 1/4 medium onion (diced) and cook, stirring occasionally, until tender, about 3 minutes.
Add 1 pound ground beef and cook, breaking the meat into small pieces with a wooden spoon, until no longer pink, about 5 minutes. Drain off excess grease.
Stir in the entire recipe of your homemade taco seasoning and 1/4 cup water. Simmer, stirring occasionally, until the mixture has thickened, about 3 minutes. Remove from heat and drain any excess liquid if needed. Set the filling aside.
Wrap 20 corn tortillas in a damp paper towel and place on a plate. Microwave for 1 minute total, flipping the stack halfway through, or until the tortillas are warm and pliable. Keep them covered while you assemble the taquitos.
Working one tortilla at a time on a flat surface, place about a heaping tablespoon of the seasoned beef mixture in the center of each tortilla. Top with about 1 tablespoon shredded Mexican blend or cheddar cheese.
Roll each tortilla tightly around the filling, rolling seam-side down. Use toothpicks to secure rolls if needed. Continue until all taquitos are assembled.
To bake: Preheat the oven to 425°F. Line a large baking sheet with parchment paper. Arrange the taquitos in a single layer, seam-side down and not touching. Lightly spray the tops with cooking spray or brush with avocado oil. Bake for 15–20 minutes, turning once if desired, until crispy and golden brown.
To fry: Pour oil (enough to be about 2 inches deep) into a deep skillet and heat over medium-high until shimmering and about 350°F. Fry 3–4 taquitos at a time, seam-side down, turning with tongs so all sides get crisp, about 3–5 minutes total per batch. Transfer fried taquitos to a paper towel–lined tray to drain. Repeat with remaining taquitos, adjusting oil temperature as needed.
To air fry: Preheat the air fryer to 400°F. Place taquitos in a single layer in the basket (you will need to work in batches). Lightly spray the taquitos with cooking spray, air fry 5 minutes, flip and spray again, then air fry 2 more minutes or until crispy. Transfer finished taquitos to a plate and repeat with remaining batches.
If you used toothpicks, remove them before serving.
Serve the taquitos with desired toppings: shredded lettuce, diced tomatoes, sour cream, salsa, and guacamole.