Slice cucumber in half lengthwise; scoop out the seeds. Cut into thin slices. In a small bowl, toss with 1 teaspoon of salt, and let stand in a colander to drain.
Peel the onion, slice into rounds, cut each round in half.
Wash and trim the radishes. Cut into halves or slices.
Wash the pepper, seed it, and cut into strips.
Wash the fennel, trim and cut into strips.
Wash the baby carrots, and cut into halves or quarters.
Toss all the vegetables save the cucumber in a large bowl, then pour boiling water over them to cover them. Immediately drain them in another colander, then put them back in the bowl, and add the cucumber.
Heat in a small pan the seeds until the mustard seed starts to pop, then add the vinegar, sugar, 1/2 teaspoon of salt, bay leaves and peeled garlic cloves, and let this simmer for a few minutes.
Then pour this liquid over the vegetables, tossing them occasionally in it as it cools. Transfer to a large, sterile jar. If there's not enough vinegar to cover all the vegetables in the jar, top up with a little more. Cover the jar, and store in fridge.