Preheat oven to 425°F. Trim the stem ends from the zucchini, then halve each lengthwise. Use a spoon or melon baller to scoop out the seedy centers, leaving about a 1/2-inch shell all around. Reserve 1 cup of the scooped flesh, finely chop it, and set aside. Pat the zucchini boats dry with paper towels - this prevents soggy bottoms.

Brush the cut sides of the zucchini with 1 tablespoon olive oil and arrange cut-side up on a rimmed baking sheet. Season with 1/2 teaspoon salt and the black pepper. Roast for 12-14 minutes until just tender when pierced with a knife but still holding their shape. The edges should look slightly wrinkled. Remove and set aside. Leave oven on.

While zucchini par-bakes, heat remaining 1 tablespoon olive oil in a medium skillet over medium heat. Add the reserved chopped zucchini flesh and cook for 4-5 minutes, stirring occasionally, until most of the moisture evaporates and it starts to turn golden at the edges. This concentrates flavor and prevents watery boats.

Stir in the marinara sauce, dried oregano, and remaining 1/4 teaspoon salt. Simmer for 3-4 minutes until slightly thickened. The sauce should coat the back of a spoon rather than running off immediately. Remove from heat.

Blot any accumulated liquid from the par-baked zucchini shells with paper towels. Divide the sauce mixture evenly among the 8 halves, spreading to the edges. Top with shredded mozzarella, then scatter pepperoni over each. Finish with a light sprinkle of Parmesan.

Return to the oven and bake 10-12 minutes until the cheese is fully melted, bubbling in spots, and starting to turn golden brown in places. For extra color, broil for 1-2 minutes at the end - watch closely to prevent burning. Let rest 5 minutes before serving. Top with fresh basil.