• Trim the mushrooms, keeping the stems intact, and cut into ¼-inch-thick strips.
• Trim the squash, cut in half lengthwise, then on the diagonal into ¼-inch-thick strips.
• Remove the ribs and seeds from the the red pepper; cut the pepper into ¼-inch strips.
• Tear the kaffir lime leaves in half.
• Coarsely chop the cilantro.
• Strip the basil leaves from their stems; coarsely chop the leaves.
• Zest the lime. Cut it in half; juice 1 half and cut the remaining half into wedges.

• Pat the salmon dry with a paper towel and season with salt and pepper.

In a pan over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. Add the mushrooms in a single layer and season with salt. Cook until browned, 1 to 2 minutes per side. Transfer to a plate.
Add 1 tablespoon oil to the pan, if dry, and warm until hot but not smoking. Add the salmon and cook, without turning, until lightly browned but only partially cooked, 2 to 3 minutes (the salmon will finish cooking in the sauce). Transfer to the plate with the mushrooms.

If the pan is again dry, add 1 to 2 teaspoons more oil and warm over medium-high heat. Add the squash and peppers and cook until starting to soften, 2 to 3 minutes. Stir in the lemongrass paste and cook until fragrant, about 1 minute. Add the coconut milk, ¾ cup water, and the kaffir lime leaves. Bring to a boil, then reduce to a simmer.

Return the mushrooms to the pan, and nestle in the salmon, seared side up. Simmer until the fish is cooked through, 2 to 3 minutes, depending on thickness.
Remove the pan from the heat. Stir in the cilantro, basil, lime juice, and lime zest. Season to taste with salt.

Remove the kaffir lime leaves from the pan. Transfer the salmon, vegetables, and sauce to individual bowls or plates and serve with the lime wedges.