Bring a large pot of salted water to boil over high heat.
Add frozen peas. Cook until peas start to float and are tender, about 3 minutes. Using a slotted spoon, transfer peas to a large bowl, allowing water to drain back into the pot.
Bring water back to a boil and add pasta shells. Cook according to package instructions until pasta is tender but still al dente
While pasta is cooking, assemble your pea mixture. Start by setting aside about half of ½ cup mint leaves for serving; finely chop remaining mint. Add chopped mint to the bowl with peas.
Using a microplane, finely grate the lemon zest into the pea mixture, add the 2 Tablespoons of lemon juice, and 4 cloves of finely chopped garlic (I use a garlic press).
Add 1⁄2 cup cream, 2 Tbsp. oil, and 1⁄2 cup cheese to bowl with pea mixture and mash with a potato masher to break up peas. You want a mix of whole peas and smooth, mushy parts.
When pasta is finished cooking, transfer to a bowl with pea mixture (i like to reserve about ½ cup of pasta water to add into pasta to help make the sauce).
Season mixture generously with pepper and more salt, if needed, toss with a wooden spoon so hot pasta melts cheese and thickens to a creamy sauce.
Divide pasta among bowls. Top with remaining cheese and reserved mint. Drizzle with oil.