Slice the base off the stem end of the cauliflower (40 oz / 1134 g) so it sits completely flat on a surface. Fill a large pan with water to a depth of at least 1 inch and place a steaming rack or trivet inside.
Bring the water to a boil, place the cauliflower in the steamer, cover, and reduce the heat slightly. Steam until the cauliflower is barely tender, about 30 minutes, ensuring you do not overcook it.
Let it cool, then cover and chill in the refrigerator for at least 3 hours.
Combine the mashed avocados (1 cup / 8 oz / 225 g), chopped tomato (0. 75 cups / 5. 3 oz / 150 g), olive oil (2 tsp. / 0. 3 oz / 9 g), lemon juice (1 tbsp. / 0. 5 oz / 15 g), sour cream (3 tbsp. / 1. 5 oz / 43 g), ground coriander (1 tsp. / 0. 08 oz / 2. 2 g), paprika (0. 5 tsp. / 0. 04 oz / 1. 1 g), salt (0. 25 tsp. / 0. 05 oz / 1. 5 g), and black pepper (0. 125 tsp. / 0. 02 oz / 0. 5 g) in a mixing bowl and blend well.
Spread the avocado mixture evenly over the chilled cauliflower, and serve on a bed of fresh cabbage or reserved outer cauliflower leaves on a serving platter.
Cut into wedges immediately prior to serving.