Bring a large pot of salted water to a boil over high heat. Drop the frozen peas into the water for 30 seconds, then use a slotted spoon to scoop them out, place them in a bowl, and set aside. Bring the water back up to a boil and add in the tagliatelle, cook until just al dente, 8 to 9 minutes.
In the meantime, in a food processor or blender, pulse together the peas, olive oil, parmesan, garlic, mint, lemon juice, and zest. Continue blending, scraping down sides as needed, until creamy and thoroughly combined. If it has trouble blending, add a bit more olive oil or water. Puree until smooth, season with salt and pepper.
Add the tagliatelle and pesto back to the pot, stir continuously until the pasta is evenly coated in the sauce. Taste and season with salt, divide onto plates, top each serving with a dollop of creme fraiche and few turns of coarsely ground black pepper.