Heat the olive oil or butter in a 10-inch sauté pan over medium-high heat and sauté the mushrooms and diced onions. Cook until the mushrooms are limp and the onions are light brown.
Add the velouté, turkey medallions, Parmesan cheese, rosemary, salt and pepper. Bring to a simmer and cook 3–4 minutes.
Arrange the crêpes into a non-stick pan and divide the hot turkey filling equally over half of each crêpe. Cover the filling with the other half of the crêpe and top each filled crêpe with one slice of Swiss cheese.
Place into a hot oven or under a salamander until the cheese melts.
Arrange onto a serving plate (carefully removing from the pan with a wide spatula) then sprinkle with the chopped chives.
Serve with fluffy scrambled eggs garnished with sliced green onions, also great with toasted French bread.