Step 1

Place a rack in the center of your oven and preheat to 400 degrees F.

Step 2

Bring a large pot of salted water to a boil. Cook pasta until barely al dente according to package instructions. You want it to still be firmer than you would ordinarily eat it, as it will cook further in the oven. Drain, toss with a bit of olive oil to prevent sticking, then set aside.

Step 3

Pulse the bread slices in a food processor until coarse crumbs form. Measure 3/4 cup crumbs into a large mixing bowl. Add the ground turkey, turkey sausage, egg, salt, Parmesan, and parsley. With your fingers or two forks, mix lightly until the ingredients are combined, being careful not to compact the meat.

Step 4

Form the mixture into 2-inch balls. You should have about 28 or so balls total.

Step 5

Heat 1 1/2 tablespoons olive oil in a large, deep, oven-proof skillet over medium-high. Add the meatballs, then cook, turning a few times, until all sides are browned, about 10 minutes. With a slotted spoon, transfer the meatballs to a plate.

Step 6

To the skillet, add the remaining 1/2 tablespoon olive oil. Add the onion and cook until beginning to brown and soften, about 4 minutes, then add the garlic, oregano, and red pepper flakes. Cook just until fragrant, about 30 seconds, then add the jarred pasta sauce and spinach. Return the meatballs to the pan and let simmer in the sauce until they are cooked through, about 20 minutes.

Step 7

Once the meatballs are cooked, add the drained pasta and the 4 ounces shredded mozzarella to the skillet with the meatballs and sauce, then gently stir to combine. Top with the remaining 4 ounces sliced mozzarella cheese, then transfer the skillet to your oven.

Step 8

Bake until the cheese is melted and lightly crisp on top and the edges are bubbling, 15-20 minutes. Let rest for 5 minutes, then enjoy!