Chop the yellow onion and mince the garlic. Heat a large pan over medium heat and add the olive oil. Add the garlic and onion, cooking until the onion is translucent.
Add the beef and cook until browned, about 7 to 10 minutes. Drain the grease.
Mix in the water and taco seasoning. Set aside.
Spray a 9x13-inch pan with cooking spray.
Arrange all the taco shells in the baking pan, pressed against each other so they stand up. Spoon beef filling into each taco shell and sprinkle with cheese.
Bake uncovered for 8 to 10 minutes, or until the cheese is melted and the taco shells are slightly browned.
Prepare the toppings by chopping the tomato, red onion, and cilantro. Slice the jalapeno.
Remove tacos from the oven and garnish with toppings. Squeeze on fresh lime juice, if desired. Enjoy!
Notes
Use a cookie scoop to help you fill the taco shells without any messes.
Use a 9X13 pan and make sure you stand the taco shells upright which will help prevent them from tipping while baking.
Add a little cheese under the beef filling to help seal the bottom of the shell and prevent it from getting soggy.
Don't overfill the shells. The filling could spill over and get messy as they bake.
Prep the toppings while the tacos bake so everything is ready to go as soon as you pull the casserole dish out of the oven.