Combine raspberries and juice of 1/2 lemon in a small sauce pan and heat over low. Mash berries with a fork and stir until broken down to a consistency you’re happy with! Taste, add stevia if you’d prefer it more sweet and less tart.
Add chia seeds and mix well. Transfer jam into small jar and refrigerate for 1 hour to set.
I encourage you to skip the sweetener all together, by immersing yourself into the real flavors of foods (which aren't intended to be totally sweet) with time you won't need sweeteners and will simply enjoy foods in their most natural flavors.