Since you are making a Tex-Mex Casserole, this Four Bean Salad recipe should go well with it.
Four Bean Salad
1 can Yellow Wax Beans
1 can Cut Green Beans
1 can Garbanzo Beans
1 can Red Kidney Beans
1 medium red onion, chopped
1 small green bell pepper, chopped
1/2 cup white sugar
1/3 cup corn oil (Make sure it is corn oil)
2/3 cup white vinegar
Dash garlic salt
Salt and pepper to taste
Drain and rinse all beans in cold water
Combine all ingredients and chill for several hours to blend flavors (I usually make this the day ahead of serving it.) Turn several times to cover all the beans
Note: you can adjust the amount of sugar to your taste; I usually use only 1/4 cup sugar.