Preheat and prep the pan: Heat the oven to 400°F (200°C). Line a large baking sheet or 9x13-inch dish with parchment for easy cleanup.

Prep the zucchini boats: Trim ends, slice each zucchini lengthwise, and scoop out the centers with a spoon. Leave about 1/4-inch border so they hold their shape. Chop about half of the scooped-out zucchini and set aside for the filling; discard any excess watery bits.

Season and par-bake: Brush the zucchini halves with olive oil, sprinkle with salt and pepper, and place cut side up on the pan. Bake for 10–12 minutes to soften slightly. This helps prevent sogginess later.

Brown the sausage: While the zucchini bakes, heat 1 tablespoon olive oil in a large skillet over medium. Remove sausage from casings if needed. Cook, breaking it up with a spatula, until browned and no longer pink, about 6–8 minutes. Drain excess fat if there’s a lot, but keep 1–2 tablespoons for flavor.

Sauté aromatics: Push sausage to one side of the pan. Add onion to the open space and cook 3–4 minutes until softened. Stir in garlic and the chopped zucchini from step 2; cook 1–2 minutes longer until fragrant.

Build the filling: Stir in tomato paste, crushed tomatoes or marinara, Italian seasoning, and a pinch of red pepper flakes. Simmer 2–3 minutes to thicken slightly. Taste and season with salt and pepper. Turn off heat and fold in half of the mozzarella, half of the Parmesan, and the fresh parsley.

Stuff the boats: Remove par-baked zucchini from the oven. Spoon the sausage mixture evenly into each boat, mounding it a bit. Top with remaining mozzarella and Parmesan.

Bake until bubbly: Return to the oven for 12–15 minutes, or until the cheese is melted and lightly golden and the zucchini is tender.

Finish and serve: Let cool for a few minutes so the filling sets. Garnish with extra parsley or basil. Serve warm with a simple side salad or roasted veggies.