Cut the rhubarb into 1/2-inch pieces and hull and quarter the strawberries. Combine the prepared rhubarb, strawberries, and honey in a large pot and bring to a boil over medium-high heat, stirring occasionally. Once boiling, reduce heat to medium and simmer for 5 minutes to soften the fruit and begin breaking down its structure.

Remove the pot from heat and mash the softened fruit with a fork to your desired texture—I prefer leaving some berry pieces intact for a rustic jam, but mash the rhubarb well since it's more fibrous. Stir in the chia seeds and lemon juice, which will brighten the flavor and help the jam set as the chia absorbs liquid.

Return the pot to low heat and cook for 20 minutes, stirring occasionally to ensure even thickening and prevent sticking on the bottom. The jam will continue to thicken as it cools, so don't worry if it seems slightly loose at this stage. Remove from heat and let cool completely before transferring to containers—this usually takes about 30-45 minutes at room temperature, though you can speed this by chilling in the refrigerator if needed.