Preheat oven to 350F (175C).
In a small bowl, combine tuna, artichoke hearts, mushrooms and Swiss cheese; toss together.
Split croissants horizontally.
Open and place on a baking sheet.
Fill croissants with tuna mixture.
Bake 10 minutes.
In a small saucepan, heat together cream cheese, sour cream and milk.
Stir constantly until smooth and bubbly.
Remove from heat.
Cover luncheon plates with spinach or romaine lettuce.
Place 1 croissant on each plate.
Remove top and set at an angle at back of bottom part.
Spoon warm cream sauce over filling.
Sprinkle with chives or green onion.
Arrange several radish slices beside sandwiches.