Pick over and rinse the split peas, then place them in a large saucepan with the onions and enough water to cover. Bring to the boil, then reduce the heat and simmer for 30-45 minutes until the split peas are thick and mushy (the exact time will depend on the age of the peas). If there is still some water remaining, drain it off before transferring the peas to a bowl.
Beat in the garlic, lemon juice and oil until thick and well blended. Leave to cool, then add salt and pepper to taste and garnish with paprika.