Halve the squash and place cut side up on a damp paper towel in a microwavable dish. Microwave on high until tender, about 15 minutes.
Meanwhile, in a large saucepan, stir together the marinara and peas and warm over medium heat for about 5 minutes. Using a fork, scrape the strands of squash into the marinara and peas.
Bring to a simmer and cook until the sauce is no longer watery, 5 to 7 minutes; remove from the heat. Stir in the ricotta and season with salt and pepper. Divide among 4 bowls and top each portion with some of the parmesan.