01 - Place the peeled and diced potatoes in a large pot. Cover with salted water and bring to a rolling boil over high heat. Reduce to a simmer and cook for approximately 15 minutes, or until the potatoes yield easily when pierced with a fork.
02 - While the potatoes cook, heat a small skillet over medium heat. Add the diced red bell pepper, seeded jalapeño, and minced garlic. Sauté for 3 to 4 minutes until the vegetables have softened and become fragrant. Remove from heat and set aside.
03 - Drain the cooked potatoes thoroughly in a colander, then return them to the pot. Using a potato masher, work the potatoes until smooth and free of large lumps.
04 - Add the milk, sour cream, and shredded cheddar cheese to the mashed potatoes. Stir vigorously until the mixture becomes creamy and the cheese begins to melt into the potatoes.
05 - Gently fold the sautéed pepper mixture, sliced green onions, ground cumin, smoked paprika, chili powder, salt, and pepper into the creamy potatoes until evenly distributed throughout.
06 - Taste the finished mashed potatoes and adjust the salt, pepper, or spice levels as needed to suit your preference.
07 - Transfer the Tex-Mex mashed potatoes to a warm serving bowl. Garnish with freshly chopped cilantro if desired and serve immediately while hot.