Step 1

Preheat the oven to 375 degrees F (190 degrees C).

Step 2

Bring a large pot of salted water to a boil. Add shells and cook, stirring occasionally, until tender yet firm to the bite, about 9 minutes.

Step 3

While the shells are cooking, heat olive oil in a large pan or skillet over medium-high heat. Add meatless ground beef and cook and stir until brown, 2 to 3 minutes. Add tomatoes, onion, garlic, 1 tablespoon Italian seasoning, salt, and pepper. Simmer for 2 minutes; add spinach and simmer until spinach is wilted, about 2 minutes more. Taste and adjust salt and pepper if needed. Remove from heat and mix in ricotta cheese and egg until fully incorporated.

Step 4

Pour 1/2 cup marinara sauce into the bottom of a 12-inch cast iron skillet or a 9x13-inch baking dish and spread out with the back of a large spoon.

Step 5

Drain cooked shells. Stuff each with about 1 1/2 tablespoons of the "meat" mixture. Arrange in the skillet or baking dish. Pour remaining marinara over the top. Sprinkle with Parmesan and mozzarella cheeses. Sprinkle with remaining Italian seasoning and more black pepper.

Step 6

Bake in the preheated oven until cheese is golden and bubbly, 35 to 45 minutes.