Put the water, steel cut oats, and cinnamon in the Instant Pot. Stir the mixture, then cover the pot and seal it. Cook on manual high pressure for 3 minutes.
While the oats are cooking, place the fruit in a medium pan along with the maple syrup and lemon juice. Cover and cook over medium heat until the fruit defrosts, about 2 minutes. Set aside and keep covered so it stays warm.
When the oats are done cooking, let the pressure release naturally (about 10 minutes), then divide the oatmeal among 4 bowls. Top with the warm fruit mixture and drizzle with additional maple syrup if desired.