Bring a large saucepan of water to the boil and cook green beans for 2-3 minutes until they turn bright green. Remove with a slotted spoon and plunge into iced water to stop the cooking process.
Add broad beans to the same pan and cook for 1 minute until softened and green, then plunge into iced water. Once beans are cool, drain well and pat dry.
Slice corn kernels off the cobs and combine with beans and tomatoes.
In a separate bowl, mix lime juice and olive oil and season to taste. Toss through vegetables.
Heat the grill (broiler). Top each slice of sourdough with a sliced round of cheese (about 1 cm thick). Put under the grill for a few minutes until bread is warm and cheese is melted.
Spoon corn salad over rocket and top with sourdough cheese slices.
Frozen broad beans can be used also, just reduce the quantity to 300 grams.