Preheat your oven to 400 degrees F and spray a 9x13 baking dish with cooking spray.
Slice the zucchinis in half lengthwise, then use a spoon to scoop out the center seeds, making a long well in each zucchini. Place the hollowed zucchini halves in the greased pan.
Sprinkle the zucchini with the salt and set them aside.
Add the ground beef to a large skillet and cook over medium-high heat until it is no longer pink (about 8 minutes). Break up the beef as it cooks with a wooden spoon, making small crumbles.
Drain the fat from the pan of cooked beef and discard.
Add the bell pepper, onion, and garlic to the pan and stir. Cook for 4 minutes to soften the onions and peppers.
Stir the marinara sauce into the pan of beef and add the basil. Bring the mixture to a simmer and cook for 2-3 minutes, stirring occasionally.
Use a paper towel to pat the zucchini boats dry, absorbing the water on the zucchini.
Brush the zucchini with the olive oil.
Scoop the beef and sauce into each zucchini boat, stuffing each zucchini as much as possible.
Bake the stuffed zucchini for 15 minutes, then remove the pan from the oven, sprinkle the zucchini with the parmesan and mozzarella cheese, and return the pan to the oven. Bake the zucchini for another 10 minutes. The cheese will be melted and starting to brown.
Enjoy the zucchini while hot as a complete meal!