1Butter a 7 by 11 inch baking pan. Line a baking sheet with parchment paper. Set aside.
Put the flour, oatmeal, brown sugar, baking powder, salt and cinnamon in a food processor and pulse to blend, about 20 seconds. Add the butter and pulse to cut the butter into the dry ingredients until you have a crumbly mass - not dry but not sticking altogether. Toss the berries in a bowl with the sugar, cornstarch and lemon juice.
Spread or pat half of oatmeal mixture into pan. Spread on berries and sugar/cornstarch mixture. Top, as evenly as you can, with remaining oatmeal mixture and press slightly. Chill 30 minutes.
Preheat oven to 350 F. Bake 30-40 minutes until fruit starts to bubble. Cool in pan very well before cutting or refrigerate 2-3 hours before cutting