Heat a medium skillet over medium heat.
Add the ground beef to the skillet and cook, breaking it up with a spatula, until no longer pink, about 5–7 minutes.
Sprinkle the taco seasoning over the cooked beef, stir to combine, and cook 1–2 minutes more to let the seasoning toast.
Remove the skillet from heat and drain any excess fat if desired.
Warm or lightly brown the tortillas if you prefer.
Assemble tacos by dividing the seasoned beef among the tortillas and topping with arugula (or lettuce), halved grape tomatoes, sliced red onion, sliced avocado, pepper jack cheese, sour cream, and salsa.