Spicy Black Bean & Lentil Salad

• 2 lentils (cooked red)
• 1 lemon
• 1 butterhead lettuce
• 525 gr black beans (cooked)
• 65 gr carrots (grated)
• 120 ml rice vinegar
• 45 ml olive oil
• 26 gr garlic (minced)
• 5 ml dry mustard
• 3 gr salt