1. Heat oil in large skillet over medium-high heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook for another minute. Add peppers, oregano, cumin, tomatoes, chicken broth and salt. Bring to simmer and continue to cook, stirring occasionally, until slightly thickened, about 10 minutes.
2. Carefully transfer to blender and puree until smooth. Return sauce to skillet and add chicken, tossing to coat. Continue to cook over medium-low heat until thickened, about 10 minutes. Taste and add additional salt if necessary.
3. Serve on corn tortillas and top with sliced avocado, cilantro, red onion, and cheese. Finish with a squeeze of lime.