Preheat an outdoor grill or preheat a broiler to high and position a rack on the second shelf. Dress the corn with a little oil and season with a sprinkle of chile powder, salt and pepper. Grill or broil the corn, turning occasionally, until tender and evenly charred, 12 to 15 minutes. Invert a small bowl in a larger bowl. Using tongs, remove the corn from the grill or broiler and steady the ears upright, 1 at a time, on the inverted bowl. Using the back of a knife, scrape the kernels from the cobs. Dress with the lime juice.
In a small saucepan, bring the cream, chipotle, adobo sauce and lime peel to a boil over medium heat on the stovetop only (cream requires a babysitter and the grill heat is too high). Lower the heat to a low, slow boil and cook until reduced slightly.
In another small saucepan, combine the refried beans and 1/4 cup water on the grill or over medium-low heat. Heat through and remove from the grill.
While the beans heat, line up your toppings. Char the tortillas on the grill or under the broiler, then top with the beans and some of the cheese. Melt under a covered grill or the broiler for 1 minute. Save a little cheese for garnish.
Serve 2 tostadas per person. Top each tostada with a mound of corn, the chipotle cream, the remaining cheese, the lettuce, tomatoes, onion, pickled chiles and cilantro, if using.