How to Make It
In a small saucepan of boiling water, cook the corn until tender, about 4 minutes; drain and let cool. Put the corn in a medium bowl and add the rice and beans. In a small bowl, stir together the sour cream, yogurt and chipotles.
Halve the avocados and scoop the flesh into a bowl. Add the lime juice and mash until smooth. Season with salt and pepper and cover with plastic wrap.
Light a grill or heat a grill pan. Brush the onion slices with the 2 tablespoons of olive oil and season with salt and pepper. Grill the onions over a low fire for about 20 minutes, turning once, until nicely caramelized; transfer to a plate.
Brush the grill or grill pan with oil. Season the salmon with the cumin, coriander and salt and pepper. Put the salmon on the grill and cover. Alternatively, arrange the fillets on the grill pan and cover tightly. Grill the fish over a low fire for 8 to 10 minutes, or until cooked through. Transfer the fish to a plate.
Warm the tortillas on the grill for a few seconds, just until pliable. For each burrito, spread some of the grilled onions on a tortilla and top with a salmon fillet, some of the rice mixture and avocado and 2 heaping tablespoons of chipotle cream. Fold in the bottom, sides and top of the tortilla to enclose the filling and serve.