Rinse and drain the lentils thoroughly using a fine mesh sieve. Lentils do not require prior soaking.
Add them to a saucepan with 3 cups (720 ml) of water or vegetable broth and the diced carrots. Bring to a boil, then reduce to a simmer for 20–25 minutes until tender but still firm. Drain well and spread out on a wide bowl or pan to cool.
While lentils are cooking, dice the cucumber, avocado and apple into bite-size pieces, and roughly chop the almonds if needed.
In a small bowl or jar, whisk together olive oil, lemon juice, salt, pepper, and garlic powder until combined. Taste and adjust seasoning or add mustard if desired.
Once the lentils have cooled slightly, add them to a large mixing bowl with the chopped vegetables, avocado, apple, seeds, nuts, and cheese. Pour the dressing over and toss thoroughly until all ingredients are combined.
Taste and adjust with salt, black pepper or lemon juice if necessary.
Serve immediately or refrigerate for at least 30 minutes to allow flavors to meld. Refrigerate leftovers in an airtight container for up to 5 days.