You can get quite a lot of food in 850 calories. Vegetables are pretty low cal. Below is a plan I just created that is less than 850 calories
Total Cals - 836
Breakfast: 2 eggs - 156 calories
Lunch:
2 cups of spinach - 14 calories
1 cup of bell peppers - 39 calories
200 grams chicken breast - 226 calories
Snack:
1 banana - 105 calories
Dinner:
200 grams chicken breast - 226 calories
1 cup of broccoli - 31 calories
1 cup of bell peppers - 39 calories