Char peppers under the broiler, turning occasionally or over an open flame on a gas burner. Once charred and blistered, place in a bowl to cool. Peel peppers then slit them lengthwise on one side and remove seeds, forming pepper boats. Arrange on a baking sheet.
Meanwhile, heat oil in a small pan over medium-high heat, add 1 jalapeño, half the onions, the garlic, salt, pepper and cumin, and stir 2-3 minutes. Add beans and thin with 1/4 cup water; bring to a bubble then reduce heat to low.
Combine remaining jalapeño and onion with cilantro, tomatoes and salt. Stir to combine to make salsa.
Preheat broiler if you did not use it to char peppers.
Fill poblanos with beans and top with chips, salsa and cheese. Place under broiler to brown the cheese and edges of chips. The peppers will look like they are filled with nachos. Garnish with scallions and serve.