Spinach Salad with Poppyseed Dressing

1 lb. bag spinach
1/2 red onion (sliced or chopped)
3/4 lb. sliced mushrooms
2 C. cottage cheese (rinsed in mesh strainer)
3/4 lb. grated mozzarella cheese
soft bacon bits

Dressing:
1/2 C. vinegar
3/4 C. olive oil
1/2 C. sugar
1 tsp. salt
1/2 tsp. mustard
1 Tbsp. poppyseeds

Mix dressing and chill for an hour. Pour over dressing when ready to serve.