Add a medium pot to the stove with 1 and half liters of water in it. Leave to heat up on low heat.
Add a large pan to the stove and add the mushrooms and prosciutto slices. Cook the prosciutto just until it changes the color, then turn and take away on a large plate. Cook the mushrooms until cooked through.
In the place left empty by the prosciutto slices, add the halloumi cheese and cook on each side until lightly brown and tender. Take all aside on the plate.
Add the egg to a tea sieve to drain the excess water around the egg-white. Poach the egg in the simmering water by adding half a tbsp of vinegar and creating a vortex in the water. Leave the egg to cook on medium heat until the egg rises to the surface. Take the egg out on a paper towel, then add it on top of the halloumi cheese.
Add the pesto sauce on top of the egg.
Wash and slice all vegetables as you like, then toss them in a bowl, season with salt and lemon juice.
Add everything to the plate and serve with a slice of whole-wheat toast.