What sets American cooking apart from other cuisines, with both negative and positive results, is our ability to dress up convenience foods to make them taste exotic. Sometimes it works (Julia Child adds port and fresh parmesan cheese to canned consomme') and sometimes it doesn't (hot dogs with prepackaged macaroni and cheese).

The following soup and sandwich combination, passed along by a friend from Mexico City who leads a weight-loss class, depends on convenience items--canned chilies, canned tomatoes, frozen corn--but reproduces an authentic flavor without an evening of chopping or a week of perusing cookbooks. In fact, this is the ultimate in a throw-together meal: Just watch the tortillas under the broiler to make sure they don't burn.

The meal is guaranteed to get you through the express lane of the supermarket, provided you already have staples on the shelf at home. It is presumed every kitchen has flour, sugar, salt, pepper and butter and/or cooking oil.

EXPRESS LANE LIST: garlic, scallions, canned green chilies, canned whole tomatoes, frozen corn, flour tortillas, cheddar cheese and sour cream and chicken broth (both optional). MEXICALI SOUP (4 servings) 1 tablespoon olive oil 2 large cloves garlic 1 bunch scallions 2 to 4 ounces chopped mild green chilies (or to taste) 1/8 teaspoon freshly ground pepper 28-ounce can whole tomatoes 10 ounces frozen corn 1 cup water or chicken broth Sour cream, optional

Heat olive oil in a large saucepan. Chop garlic. Trim any wilted or crushed ends from the scallions and chop them, including the green tops. Add garlic and scallions to olive oil and stir over high heat for 2 to 3 minutes (keep stirring or they will burn). Add chilies and pepper. (These chilies are fairly mild, but those sensitive to the heat might want to add with caution.) Lower heat to medium and stir 2 to 3 more minutes. Add tomatoes with their juice and 1 cup of water or chicken broth. Bring to a boil and cook about 10 minutes. Add corn and cook 10 to 15 minutes more. Serve in heated bowls with dollops of sour cream, if you like, and open-faced cheese tortillas. GRINGO CHEESE SANDWICHES (4 servings) 4 flour tortillas 6 to 8 ounces colby or monterey jack cheese, grated Toast tortillas about 5 inches away from preheated broiler for 30 seconds. Flip them and repeat (you may have to do this in 2 batches). Cover the surface of the tortillas with grated cheese and run under the broiler again until cheese melts and is bubbling.