Prepare rapidly boiling, salted water to cook pasta; cook until al dente,8 to 10 minutes for dry pasta, approximately 3 minutes for fresh. Pasta may be cooked slightly ahead of time, rinsed and oiled and then "flashed" (reheated) in boiling water or cooked to coincide with the finishing of the sauce/topping.
Cook 1/3 cup cilantro, garlic and jalapeno in 2 tablespoons butter over medium heat for 4 to 5 minutes. Add stock, tequila and lime juice. Bring the mixture to a boil and cook until reduced to a paste like consistency; set aside.
Pour soy sauce over diced chicken; set aside for 5 minutes. Meanwhile cook onion and peppers, stirring occasionally, with remaining butter over medium heat. When the vegetables have wilted (become limp), add chicken and soy sauce; toss and add reserved tequila/lime paste and cream.
Bring the sauce to a boil; boil gently until chicken is cooked through and sauce is thick (about 3 minutes). When sauce is done, toss with well-drained spinach fettuccine and reserved cilantro.
Serve family style or transfer to serving dishes, evenly distributing chicken and vegetables.