Dry roast the Sichuan peppercorns in a hot wok for 20 seconds, then lower heat and stir for about a minute until aromatic. Crush in a mortar and pestle or spice grinder. Mix with the flour and season with a pinch of salt. Set aside.
Crush the black peppercorns and reserve separately.
Heat vegetable oil in the wok on high. When just beginning to smoke, add the eggplant and shallow-fry until golden brown, then drain on paper towel.
Toss the tofu in the flour mixture and fry until golden all over, with a thin crust. Reserve and clean out the wok.
Add 1 tbsp oil to the wok. When just smoking, add onion, capsicum, chilli, garlic and crushed black pepper and stir-fry until fragrant.
Add stock, soy sauce, oyster sauce and caster sugar and reduce slightly. Check seasoning, then add the tofu and eggplant to the sauce.
Add cornflour and water mixture to thicken if desired.
Garnish with shallots and coriander and serve with rice.