Preheat oven to 400°F.
Slice zucchinis lengthwise and scoop out centers to form boats.
Place zucchini halves in a baking dish and bake 10 minutes.
Cook ground beef in a skillet over medium heat until browned.
Add onion and garlic; cook until softened.
Stir in taco seasoning, tomato paste, and water; simmer 2–3 minutes.
Season with salt and pepper.
Remove zucchini from the oven and fill each half with the beef mixture.
Top evenly with shredded cheddar cheese.
Bake 12–15 minutes until cheese is melted and zucchini is tender.
Add optional toppings before serving if desired.