Preparation

• In a small bowl, combine the mayonnaise, chipotles, lime juice, cilantro, and 1/2 tsp. salt.
• In a large skillet, heat 1 Tbs. of the oil over medium-high heat. Add the cumin and cook, stirring, until aromatic, about 15 seconds. Add the roast beef and season lightly with salt. Cook just until browned in spots, 1 to 2 minutes, then transfer to a plate. Add the remaining 1 Tbs. oil and the bell pepper and poblano to the pan, and cook, stirring occasionally, until fragrant and beginning to soften, about 2 minutes. Add the onion and a pinch of salt. Cook, stirring occasionally, until tender and browned in spots, 6 to 8 minutes. Transfer the mixture to a bowl.
• Heat a panini press on high or a nonstick grill pan over medium-high heat.
• Spread 2 Tbs. of the mayonnaise over two slices of bread, and top with the roast beef. Top each with the pepper and onion mixture, 3 slices of cheese, and the remaining bread slices. Spread 1 Tbs. of the mayonnaise on top of each sandwich and place the sandwiches, mayonnaise side down, in the panini press or the grill pan. Spread 1 Tbs. of the mayonnaise mixture on top of each sandwich and close the press. Cook until nicely browned and the cheese has melted, about 5 minutes. (For a grill pan, weight the sandwiches with a clean heavy pan, and apply the mayonnaise to the second side just before flipping once.) Let rest for a few minutes before slicing and serving with the remaining mayonnaise.