1-3/4 cups chicken broth, divided
2 poblano chiles, roasted, peeled, seeded and deveined
2 Tbsp. chopped onions, divided
1 can (8 oz.) tomato sauce
1 Tbsp. chopped canned chipotle peppers in adobo sauce
1 tsp. dried oregano leaves
12 corn tortillas (6 inch), warmed
3 cups shredded cooked chicken, warmed