In a small pot, add lentils and water, cover and bring to a boil. Reduce heat to low and cook for 10 minutes. Set aside.
In the meanwhile, add salmon to a food processor and pulse a few times until it has finely chopped texture. Do not over process into fine mush. Transfer to a large bowl.
Add onion and garlic to a food processor; process until pureed, stopping and scraping the sides of the bowl. Transfer to a bowl with salmon along with cooked lentils, egg, Dijon mustard, parsley, salt and pepper. Then mix well using your hands.
Preheat large non-stick skillet on medium heat and swirl about 1 tbsp of oil to coat. Pack 1/2 cup measuring cup with salmon mixture, using your hands form into a patty and place carefully on a skillet. Add as many patties as skillet can fit and cook for 4 minutes or until white edges appear. Carefully flip and cook for another 4 minutes. Repeat with remaining mixture, cooking in batches and adding more oil.