Serves 4 to 6
Bring salted water in a 2-gallon or larger stockpot to a boil and cook fettuccine according to package directions. When pasta is done, drain, reserving 1 cup cooking liquid. (Up to 1/2 cup additional cooking liquid may be added if pasta seems too dry.)
While pasta is cooking, begin making sauce: In a 12-inch or larger saute pan, heat olive oil over medium-high heat. Add onion, shallot, salt, and pepper and cook until onions are translucent, about 2 minutes. Add garlic, bacon and peas and cook 2 minutes longer. Add cooked drained pasta, parsley, cheese, and olive oil garnish and cook, tossing, until heated through and well combined. (If necessary, add a bit of reserved pasta-cooking water a little at a time to moisten.)
Remove pasta from heat and transfer to a large serving bowl or to individual serving bowls. Sprinkle with additional cheese and black pepper if desired. Top with chives and serve immediately.