Heat oven to 350F. Line an 8-inch square pan with parchment, leaving overhang on two sides for easy removal. Spread sliced almonds on a rimmed baking sheet and toast for 5-7 minutes until golden and fragrant. Let cool slightly.

In a large bowl, stir together oats, toasted almonds, flaxseed, and salt. Set aside.

In a medium saucepan over medium-low heat, combine honey, almond butter, and coconut oil. Stir constantly until smooth and just beginning to bubble at the edges, about 3-4 minutes. Remove from heat and stir in vanilla.

Pour the hot honey mixture over the oat mixture. Stir with a rubber spatula until every oat and almond is coated. The mixture will seem loose at first but will stiffen as it cools. Transfer to the prepared pan and press down firmly and evenly with the back of a measuring cup or damp hands. Press hard - compact bars hold together better.

Bake for 18-20 minutes until the edges turn deep golden and the center looks set but still slightly soft. It will firm up as it cools. Cool completely in the pan on a wire rack, at least 30 minutes. For cleanest cuts, chill in the refrigerator for 15 minutes, then lift out using the parchment overhang and slice into 12 bars with a sharp knife.