Combine 1/4 cup water, taco seasoning, and oil in a shallow dish or heavy-duty zip-top plastic bag; mix well. Add chicken pieces; cover or seal and chill 5 minutes or up to 12 hours.
Cook chicken and marinade in a large, hot nonstick skillet over medium-high heat, stirring often, 5 to 10 minutes or until chicken is done.
Stir together 1/2 cup salsa and remaining 1/4 cup water in a 13- x 9-inch baking dish until well blended. Spread evenly over bottom of dish.
Stir together 2 1/2 cups Monterey Jack cheese, ricotta cheese, and next 4 ingredients. Spoon 1/3 cup cheese mixture down the center of each tortilla; top with chicken, and roll up. Place tortillas, seam side down, over salsa mixture in dish. Drizzle remaining salsa over enchiladas; sprinkle with remaining 1/2 cup Monterey Jack cheese.
Bake at 350° for 20 to 25 minutes or until cheese melts. Top with sour cream; garnish, if desired.