Preheat a serving bowl with boiling water. In a large saucepan over medium-high heat, sauté onion in butter until soft, 10 minutes. Stir in salsa, bring to a boil, and remove from heat. Add cheese and stir until mostly melted, 3 minutes. Stir in yogurt and hot sauce and cook over medium-low heat until steaming (don't simmer), 5 minutes.
Drain water from serving bowl, add chile con queso, and serve with bell pepper strips and tortilla chips.