Heat oil in a skillet over medium-high heat.
Add beef to hot skillet and cook until no longer pink, stirring frequently to crumble. Drain grease if necessary.
While beef is cooking, bake taco shells according to package directions.
Slice avocado and pepper, chop onion and pineapple, and shred cheese (if necessary).
Add onion and taco seasoning to meat, and cook for 2 more minutes.
Spoon beef mixture into each taco shell. Top with spinach, sliced avocado, pepper slices, cheese, and salsa.
Serve with pineapple on the side.