In a kettle of boiling salted water cook the macaroni for 10 to 12 minutes, or until it is al dente, drain it in a colander, and rinse it under warm water. While the macaroni is cooking, in a large saucepan cook the bell peppers and the ham in the oil over moderately high heat, stirring occasionally, for 5 minutes. Reduce the heat to low, add the flour, and cook the mixture, stirring, for 3 minutes. Stir in the milk and the yogurt, bring the mixture to a boil, stirring, and simmer it, stirring occasionally, for 5 minutes. Add the Monterey Jack and the jalapeno pepper and cook the mixture over moderately low heat, stirring, until the Monterey Jack is just melted. Add the macaroni and salt and pepper to taste and stir the mixture until it is combined well.
Transfer the macaroni and cheese to a shallow flame-proof baking dish, sprinkle the taco chips over the top, and broil the macaroni and cheese under a preheated broiler about 2 inches from the heat for 3 to 4 minutes, or until the top is browned lightly.