Sauté the onions until translucent. Add the tomato puree and chipotle peppers and cook for 5 minutes. Add in the shredded chicken.
Prepare the green pico de gallo: Mix the tomatillos, red onions, serrano chili, cilantro, lime juice and season with salt and pepper to taste.
Prepare the chimichangas: Heat the flour tortillas, divide the chicken filling among the flour tortillas evenly, fold the left and right ends toward the center, then roll facing upwards to form a tight roll. Fry in oil on a medium heat seam side down and turn when golden brown. Remove from heat and drain on paper towels. Place chimichangas on a baking dish / tray, spread the top of the chimichangas with sour cream, cover with Sargento® Blends ™ 4 Cheese Southwest Slices and bake at medium high heat until cheese is completely melted, lightly browned and bubbly. Remove from oven.
Serve the chimichangas with a dollop of sour cream and green pico de gallo salsa to taste. Enjoy!