Place chicken in resealable food safe plastic bag, add dressing, seal bag and turn to coat. Marinate chicken in refrigerator about 30 minutes.
Meanwhile, to make pasta, in a 6-quart Dutch oven bring about 1/2-inch water to boiling. Add spinach; cover and cook about 3 minutes or until wilted. Drain spinach; squeeze dry. Place spinach in food processor bowl, puree. Add flour, eggs, and salt. Cover and process until mixture forms fine crumbs. With processor running, slowly pour 1 Tbsp. of the oil and enough water through feed to form dough into a ball, tube. Transfer dough to lightly floured surface. Cover, let dough rest for 3 minutes. Divide dough into 4 portions.
Dust work surface with flour. Roll dough into 1/2-inch-wide logs . Slice into 1-inch pieces. Gently roll each dough piece in a ball. Roll dough balls over a lightly floured gnocchi paddle or the tines of a fork to create oval shapes with grooves on one side. Cover pasta; let stand 20 minutes.
While pasta stands, in the 6-quart pot bring 3 quarts salted water and 1 tablespoon of the olive oil to boiling. Remove chicken from marinade; reserve marinade. Sprinkle chicken with crushed green peppercorns. In an extra large skillet cook chicken in the remaining 2 tablespoons hot oil over medium heat for 12 to 15 minutes or until chicken is no longer pink (170 degrees F), turning once. Remove chicken; cover and keep warm. Add mushrooms to skillet; cook 4 to 5 minutes or until tender. Add chicken broth and reserved marinade to the skillet. Bring to boiling. Stir in half the chervil. Remove from heat; cover and keep warm.
Add pasta to boiling water. Reduce heat slightly and boil, uncovered, stirring occasionally, for 2 to 3 minutes or until pasta floats to top. Drain pasta.
To serve place broth and pasta in bowl; top with chicken and mushrooms. Pour over warm broth mixture. Sprinkle with remaining chervil. Makes 6 servings.