Preheat oven to 200C. Grease a 26cm, heavy-based, ovenproof frying pan. Place prosciutto slices, slightly overlapping, over base and side of pan, trimming to fit if necessary.
Roughly chop white and most of green part of onions, then roughly chop with all but thick stems of dill. Place half each of the onions and dill in a large bowl. Reserve remainder. Add rice and eggs to onion mixture, then crumble over three-quarters of the feta. Using a whisk or fork, whisk to combine. Season with salt and pepper. Pour egg mixture into lined pan, then cook over medium heat for 5 minutes.
Meanwhile, halve pumpkin widthwise and reserve seed end for another use. Cut skin from remaining pumpkin and discard, then cut into 7mm cubes (alternatively, coarsely grate). Place in a bowl and toss with 1 tablespoon oil.
Scatter pumpkin mixture over egg mixture, then crumble over remaining feta. Transfer pan to the top shelf of the oven and cook for 15 minutes.
Meanwhile, to make tomato salad, roughly chop tomatoes and place in a bowl with reserved onions and dill. Squeeze over juice from lemon, add remaining 2 tablespoons oil, then season. Gently toss to combine.
Turn oven to the grill setting and cook tart for a further 5 minutes or until egg is set and pumpkin and feta are golden.
Serve tart with tomato salad.