Step 1

Cut 4 bell peppers and 1 poblano chile in half lengthwise. Using your fingers, pull out stems and ribs, then tap out seeds. Slice lengthwise into ¼" strips.

Step 2

Peel 3 onions and cut in half through root end. Cut a V-shaped notch into root to remove. Slice each half into 3 lengthwise wedges.

Step 3

Peel 6 garlic cloves and thinly slice.

Step 4

Slice 3 rolls lengthwise without cutting all the way through (so 2 sides remain attached).

Step 5

Place 2 lb. sausages in a large straight-sided skillet and cover with cold water just until sausages are submerged. Heat over medium-high and cook, uncovered, just until water reaches a gentle boil, 6–8 minutes. Remove from heat. Transfer sausages (they will be fully cooked) with tongs to a plate; set aside. Dump water from skillet; reserve skillet.

Step 6

While sausages cook, heat 2 Tbsp. oil in a large Dutch oven over medium. Add onions and garlic and cook, stirring often, just until onions are beginning to soften, 5–8 minutes.

Step 7

Add bell peppers, chile, and another 1 Tbsp. oil to pot; season generously with salt and pepper. Stir to combine, then increase heat to medium-high. Cover and cook, uncovering to stir occasionally, until peppers are tender, 10–15 minutes.

Step 8

Create a clearing in the middle of the pot and add 2 Tbsp. tomato paste. Stir paste until darkened in color and is sticking to bottom of pot, about 3 minutes.

Step 9

Add ⅓ cup vinegar and stir to dissolve paste and combine with peppers and onions. Cover and cook, stirring occasionally, until peppers and onions are very tender, 8–10 minutes longer. Season with more salt and pepper.

Step 10

Meanwhile, slice sausages in half lengthwise.

Step 11

Heat remaining 2 Tbsp. oil in reserved skillet over medium-high. Add half of sausages cut side down and cook, pressing down to ensure full contact with pan, until cut sides are browned, about 3 minutes. Transfer back to plate and repeat with remaining sausages.

Step 12

Divide half of peppers and onions mixture among rolls, then arrange seared sausage halves over.

Step 13

Top with remaining peppers and onion mixture. Cut sandwiches in half crosswise and serve.