Cook the spaghetti squash in the oven at 425 degrees F (218 degrees C), according to the instructions here.
Meanwhile, heat the remaining tablespoon of oil in a large pan over medium-high heat. Add the garlic and cook for about 30 seconds, until fragrant. Add the ground beef. Season with sea salt and black pepper. Cook until browned (about 10 minutes), breaking apart the meat with a spoon or spatula.
Stir in marinara sauce and Italian seasoning. Reduce heat to a gentle simmer. Simmer for about 10 minutes. If it's done before the squash is ready, cover to keep warm.
Ricotta Parmesan Cheese Layer
Meanwhile, stir together the ricotta cheese, parmesan cheese, and a tablespoon olive oil in a large bowl. (The bowl should be large enough to add the spaghetti squash strands later.) Set aside.
When the spaghetti squash is done cooking, take it out of the oven, but leave it on at 425 degrees F (218 degrees C).
Cut the squash in half lengthwise (if you cooked it whole and it is not cut yet). Place open side up onto the baking pan and use a fork to release strands.
Transfer the spaghetti squash strands into the large bowl with the ricotta and parmesan cheeses. Mix together. Season with sea salt to taste.
Stuff the spaghetti squash mixture back into the empty shells on the baking pan. Top with beef marinara mixture. Sprinkle shredded mozzarella on top. (If desired, you can create several thinner layers of each mixture, but I usually keep it simple with just one of each layer.)
Return the lasagna spaghetti squash boats to the oven for about 10 minutes, until the cheese melts.