1. Fill a large stockpot with water, add potatoes & bring to a boil. Reduce heat to medium & simmer until potatoes are fork-tender. Drain, return potatoes to stockpot & set aside.
2. Meanwhile, in a large skillet, heat oil over medium-high. Add onion & sauté 5 minutes or until translucent, stirring occasionally.
3. Stir in bell peppers & jalapeño. Sauté another 3-5 minutes. Stir in chilies & remove from heat.
4. Add milk & yogurt to the potatoes. Mash thoroughly. Add cheese, onion mixture & chipotle pepper to stockpot. Mix well. Add additional milk if needed.