Cook the cheese spinach tortellini in salted water and according to package directions.
Meanwhile, in a medium-size skillet, melt the butter and add the canned peas. Season with salt and pepper and cook until warm. If using frozen peas, cook a bit longer. They need to be soft but not mushy.
Once the tortellini are cooked and drained, return them to the cooking pan and add the peas and mascarpone. Mix and fold the pasta with the sauce to soften it.
Serve immediately with some freshly grated parmesan cheese.