Whisk olive oil, vinegar, mustard, salt and pepper together.
Clean and cut the salad vegetables. Dice the feta. Toss these along with the olives with the dressing, and set aside.
Bring salted water to a boil, and cook pasta according to package instructions until al dente.
In the meantime, measure out the cheese and finely mince the garlic.
Once pasta is done, drain it. Melt butter in the pan, sweat garlic and black pepper until aromatic.
Add flour to the pan and stir into the butter. Cook for 1 or 2 minutes.
Add milk to the roux, stirring well. Simmer briefly until thickened.
Turn off the heat. Add pasta, crab and cheese. Stir until combined and serve.