Lit your charcoal or wood sticks.
Cut the cucumber on it's lenght in 4.
Oil your grill grates with olive oil.
Grill the cucumber for about 2 minutes and the corn on the cob for about 5 minutes.
Remove from the grill, dice the cucumber, and cut the kernels of the corn with a sharp knife.
Put the diced cucumber and the kernels in a bowl.
Add the soya sauce, the sesame oil, the sugar and the garlic powder and stir.
Brush some oil on the tuna steaks and season with salt.
Grill the steaks for about 2/2½ minutes each side.
Remove from the grill and cut the steaks in slices.
Top with sesame seeds and serve with cucumber salad.