Rinse figs and trim and discard stem and blossom ends. Coarsely chop figs. In a 3- to 4-quart pan over medium heat, stir figs, lemon juice, and granulated sugar until mixture is thick and reduced to about 2 cups, about 45 minutes. Chill uncovered until cool, about 1 1/2 hours, or cover and chill up to 2 days (see notes).
In a bowl, with an electric mixer on high speed, beat butter and brown sugar until smooth. In another bowl, mix flour, baking soda, salt, and oats. Stir or beat into butter mixture (dough will be crumbly).
Press half the dough evenly over the bottom of a buttered 9- by 13-inch baking pan.
Spread fig mixture evenly over dough. Crumble remaining dough evenly over fig mixture; pat lightly.
Bake in a 400 oven until streusel is lightly browned, 20 to 25 minutes.
Place pan on a rack to cool for about 10 minutes. While still warm, cut into 24 bars.
