Pour enough water into a pot with a steamer insert to reach about 2 inches deep. Add 1 smashed garlic clove and half a lemon to the water. Put steamer insert into the pot and bring water to a boil. Arrange artichokes in the steamer insert and place a lid on the pot. Steam artichokes until a knife easily pierces the bottom of the largest artichoke, 30 to 45 minutes.
Blend olive oil, cumin, sugar, lemon juice, and a pinch of sea salt in a blender until smooth. Add green bell pepper and tomato; blend until smooth, about 1 minute. Pour chickpeas and yogurt into the blender; blend thoroughly. Thicken dip with more yogurt, if desired. Season with sea salt; serve with the steamed artichokes.