Using a fork, coarsely mash peas in a medium bowl. Add breadcrumbs, egg, flour, garlic and tuna, then stir to combine. Season with pepper.
Heat half the tuna oil in a large non-stick frying pan over medium-high heat. Place 1/4 cup pea mixture in pan. Using a spatula, flatten slightly. Repeat to form 6 patties. Cook for 3 minutes on each side or until golden and cooked through. Transfer to a plate and cover to keep warm. Repeat with remaining oil and pea mixture to make a total of 12 patties.
Meanwhile, heat rice according to packet instructions. Transfer to a large bowl. Add salad leaves, cucumber and radish, then toss to combine. Season with pepper. To make the yoghurt ranch dressing, place yoghurt, garlic powder, onion powder, chives, dill and juice in a bowl. Season with pepper. Stir until combined. Serve fritters with salad and dressing.