Heat olive oil in a large pot over low heat. Add diced onion and cook until soft and translucent, about 7 minutes. Stir in jalapeño and garlic, sautéing for 2 more minutes until fragrant.
Mix in diced green chiles, cumin, oregano, and salt. Sauté for another 2 minutes to let the flavors combine. This step really brings out the aroma of the chiles.
Add 2–3 cups vegetable broth and canned fire-roasted tomatoes. Bring to a boil, then reduce to low heat and let it simmer. Two cups of broth will yield thicker chili; three cups make it more stew-like.
Melt butter in a small saucepan and whisk in flour to make a smooth roux. Cook for 2–3 minutes until lightly golden. Gradually add the roux to the chili, stirring constantly to thicken the mixture evenly.
If using pork, add cubed pork shoulder at this stage. Simmer until the pork is tender and flavors meld beautifully, about 2–3 hours.
Taste and adjust seasoning. Your Colorado Green Chili is ready to enjoy hot as a stew or over your favorite Mexican dishes.