1. Shuck oysters. Discard the top shell; keep oysters in the deeper bottom shell. Arrange oysters over kosher salt in a jellyroll pan.
2. Heat oil in a small skillet over high heat. Add jalapeños, and cook 2 to 4 minutes, turning occasionally, until skin is golden and blistered. Transfer jalapeños to a small bowl, and cover with plastic wrap. Let stand 5 minutes.
3. Peel and seed jalapeños; finely chop, and place in a medium bowl. Add lime zest and next 5 ingredients, stirring to combine. Top each oyster with 1/2 teaspoon butter mixture. (Store remaining butter in refrigerator.)
4. Bake oysters at 450° for 8 minutes or until the edges of the oysters begin to curl.