Bring to the boil the lentils in abundant water then simmer for around 20 minutes (check after the first 15 minutes if they are soft enough). Once the lentils are soft but carry still a bit of a bite drain the water and rinse under cold water for a minute. Set aside.
Wash and cubes the veggies (I'd recommend to deseed both the salad tomatoes and the cucumbers) and add it to a bowl with the lentils.
Season with olive oil and salt to taste.
Mix thoroughly and enjoy straight away or transfer to an air-tight container to be stored in the fridge.
Notes
This salad can be enjoyed right away or it can be stored for up to 4-5 days in the fridge.