Preheat the oven to 200 degrees Celsius (392 degrees Fahrenheit).
Peel the potatoes and celeriac and grate them coarsely.
Grate the onion and put all three components into a bowl and mix together.
Add eggs, oil, oats, flour, salt, and pepper, and stir together.
Form small round röstis (about 8 cm in diameter) by taking a tablespoon of the mixture for each and placing on a baking sheet with baking paper.
Press each clump together and shape into round röstis.
Bake for about 25 minutes until they are golden and crispy.
Top with salad, crème fraîche, salmon, avocado, and herbs.
Serve ?