Bring a large pot of salted water to a boil. Heat the olive oil in a large skillet over medium-high heat. Add the onion and garlic and season with ½ teaspoon salt and a few grinds of pepper. Cook, stirring occasionally, until the onion is tender and lightly browned, about 8 minutes. Add the marinara sauce, Italian seasoning and salt and pepper to taste. Stir, then reduce the heat to low and simmer until beginning to thicken, 10 to 15 minutes. Meanwhile, break each lasagna noodle into 3 or 4 pieces (they don’t have to be even). Add to the boiling water and cook, stirring frequently to prevent sticking, until tender, 8 to 10 minutes. Reserve 1 cup cooking water and then drain. Add the butter and parmesan to the sauce and stir until it’s all combined and melted. Throw in the cooked lasagna noodles and ½ cup of the reserved cooking water; stir to combine, adding the rest of the reserved cooking water as needed so the noodles are well coated and a bit saucy. Add the mozzarella and stir until softened but not fully melted. Remove the skillet from the heat and dollop the ricotta all over the top. Sprinkle with basil leaves.