Recipe(tried): Mexican Salad with Avocado Dressing

Dressing that I always use in the summer for large groups. All
this discussion today, made me remember it in the middle of
winter (yes, it is still winter here, about 6 in. worth still
on the ground - 6 have melted since Wed.) Anyway, I digress.

Mexican Salad W/Avocado Dressing

6 C shredded iceberg lettuce
3 tomatoes, cut into wedges
1/2 C sliced ripe olives
1 small purple onion, sliced & separated into rings
2 T chopped fresh cilantro (my vote) or parsley

Place shredded lettuce on a large serving plate. Arrange
tomato wedges, sliced olives & onion rings on lettuce,
sprinkle w/cilantro. Serve w/avocado dressing. Yield: 10 serv.

Avocado Dressing

1 ripe avocado, peeled & mashed
3/4 C sour cream
1 1/2 T lime juice
1/2 tsp ground cumin
1/4 tsp salt
1/4 tsp ground red pepper
2 cloves garlic, crushed
2 T vegetable oil

Combine first 7 ingredients in a mixing bowl; beat
at medium speed of an electric mixer until smooth. Add
oil, 1 T at a time, beating until well blended. Cover
& chill up to 24 hrs. Yield: 1 1/2 C.

Do you think you could substitute yogurt for sour cream?
I am not a yogurt eater (have never even tasted it), so
I don't know.