Whisk the olive oil, balsamic vinegar, mustard and honey in a small bowl until emulsified. Add salt and poppy seeds, stir in salt and poppyseeds. Set aside.
Place arugula on a platter, cover with cucumbers and watermelon. Sprinkle with feta.
Make a stack out of the basil leaves. Roll them in either direction and thinly slice them to make ribbons. Toss evenly over the salad.