Put the serving plates in the oven at the lowest setting to keep the ham slices warm while making the sauce.
Melt half of the butter in a pan. Add the ham slices then heat over low heat until they are golden-coloured, about 1-2 min per side. Set the ham slices aside on the warmed plates and keep warm in the oven.
Add the remaining butter to the pan. Add the pineapple slices to the pan, then heat until they are golden-coloured, about 1-2 min per side. Arrange the pineapple slices on top of the ham then keep warm in the oven.
Mix the cornstarch with the lemon juice in a small cup. Pour a few spoonfuls (about 2-3 tablespoons per serving) of the juice from the pineapple can into the pan. Add the cornstarch mixture, bring to a boil, then reduce a few minutes until a syrupy sauce consistency is obtained.