Thinly slice the celery at a sharp diagonal. Tear up the leafy greens, thinly slice the radish, chiffonade cut the basil and mint.
In a large bowl, grate in the garlic cloves, then grate in the zest from half the lemon, about a teaspoon. Add the juice from the lemon, the olive oil, the vinegar and red pepper flakes. Whisk to combine then add in all the vegetables. Toss to coat, season with salt and pepper. Taste and add more vinegar, salt and pepper as you see fit.
In a small pan over medium heat, toast the poppy seeds for 4-5 minutes, or until they are noticeably nutty and fragrant. Add these into the salad and toss.
To serve, tear the stracciatella on top of the salad, creating long creamy lines of cheese. Top with more lemon zest, black pepper and olive oil. Serve with crusty bread!