Place the pak choi leaves in the base of a large steamer and place the fish on top.
Top with the lemon slices, chilli and ginger. Cover with a tight-fitting lid and sit over a pan of lightly boiling water. Steam for 10 minutes until the fish is cooked through.
Meanwhile, cook the rice according to pack instructions. Drain and stir through the chopped coriander.
Mix the sesame oil and soy together and drizzle over the fish. Serve the fish and pak choi with the coriander rice.