Heat the peanut oil in a small skillet over high heat. Add the jalapeños and cook until the skin is golden brown and blistered, about 1 minute. Carefully turn the jalapeños and cook an additional 1 to 1 1/2 minutes or until the entire jalapeño is blistered. Transfer the jalapeños to a small bowl and cover with plastic wrap. Allow the jalapeños to stand for 5 minutes. Peel and discard the blistered skin and remove the stems and seeds. Finely chop the jalapeños and place in a mixing bowl. Add the lime zest, juice, cilantro and butter to the jalapeños and stir, using a rubber spatula, until mixed well. Season the butter mixture with the salt and pepper. Set aside at room temperature.
Preheat the oven to 450°F.
Sprinkle a jelly roll pan with an even layer of kosher salt, about 1/4-inch thick. (This will keep the oyster shells from rolling around on the pan.) Shuck the oysters and place in an even layer on the prepared pan. Spoon a rounded 1/2 teaspoonful of the butter mixture into the center of each shucked oyster. The remaining butter will keep, refrigerated for up to 1 week or frozen for up to 3 months. Place the pan in the oven and bake at 450°F for 6 1/2 to 7 minutes or until the edges of the oysters begin to curl. Remove from the oven and set aside until the shells are cool enough to touch, about 5 minutes. Serve immediately.