Place a saute pan over medium heat. Add olive oil and onion, saute for 4-5 minutes, and add garlic until it begins to lightly brown. Add the cannellini beans and mix together for 2 minutes. Remove from the heat.
In a food processor or high-speed blender, puree the beans, garlic, onions, salt, and lemon juice. Blend on high or process for about 2 minutes, until creamy.