Fry onion at low heat. Add chili flakes if desired. Fry until onions are soft/translucent. Add tomato paste and let it "fry off". Add cream. Let it cook for 2-5 minutes until it thickens a bit. Add salt/pepper/sugar/thyme to taste. Add trout and peas and stir. Add in fettuccine and stir.
Serves two persons