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.
If you don't have a steamer, use a large pot with your colander as your steamer basket, but don't forget to put the lid back on! The lid does not need to fit tightly for the artichokes to still cook.
More sugar may be needed depending on acidity of tomato, but only add 1 pinch at a time.
Dip can also be made ahead of time. Tightly covered, it will keep for about 1 week in the refrigerator.