Zest lemon over the fillet, then slice the lemon and arrange lemon slices over the fillet.
Grill salmon, skin side down, 20 minutes or until flesh is opaque and can be flaked with a fork. Briefly turn the fillet over, flesh side down, so that the salmon and lemons get a quick sear, about 1 minute.
Remove salmon to a plate. Remove and discard skin and break salmon up into large chunks.
Add fettuccine noodles and salt to boiling water, and cook until al dente, about 8 minutes.
Scoop out 2 cups of the pasta water and reserve.
Drain pasta and quickly return to the pot over low heat, along with butter and cheese, and toss until butter is melted.
Add pasta water a little at a time, tossing, until a creamy sauce is formed and is the consistency that you like.
Remove from heat, add salmon and peas and toss, adding more pasta water to thin the sauce if desired.
Serve immediately, sprinkled with fresh dill and with the grilled lemon slices for garnish.
The salmon fillet can alternatively be cooked in the oven instead of grilling. Bake at 400° on a parchment-lined baking sheet approximately 15 - 20 minutes.Thawed, frozen peas can be substituted for fresh peas.