Bring a pot of salted water to boil and blanch the peas for 2 minutes, then immediately transfer to ice water to preserve their color. Drain and set aside.
In a large pot, heat a splash of vegetable broth over medium heat and sauté the garlic for 1 minute until fragrant.
Add the cucumber, lettuce, blanched peas, and remaining vegetable broth to the pot. Bring to a simmer and cook for 10 minutes until vegetables are tender.
Remove from heat and stir in the fresh mint leaves and lemon juice.
Using an immersion blender or regular blender, puree the soup until completely smooth and creamy.
Season with salt and pepper to taste, and serve warm or chilled with extra mint leaves for garnish.