1Place chicken in pan of boiling water to cover and simmer 15-20 minutes. Remove from heat, drain, cool, and shred chicken.
2In skillet, melt butter over medium heat, cook onion until just soft, 5-8 minutes. Transfer to large bowl.
3Add chicken, cheddar cheese, green chiles, salsa, cilantro, and cumin. Season with salt and pepper to taste and mix well.
Note: You can do this much a day ahead and store in the refrigerator.
4Preheat oven to 350 degrees. Grease a 10x15x2 inch pan or 2 smaller pans.
5Place 1 flour tortilla on flat surface and place about 1/3 cup chicken mixture along one edge. Roll up from filling side and place seam side down in prepared pan. Repeat process with remaining chicken mixture.
6Sprinkle Monterrey Jack cheese over enchiladas, combine cream and chicken broth and pour over enchiladas. cover pan with foil and bake 30 minutes. Remove foil and continue baking 10 more minutes or until thoroughly heated through. Garnish individual servings with avocado, tomato and cilantro, if desired.