Heat oven to 400degreesF. Place paper baking cup in each of 12 regular-size muffin cups, or grease (or use cooking spray) bottoms of muffin cups. (For best results, use paper cups.)
In medium bowl, stir muffin mix, flaxseed, cranberries, walnuts, water, oil and eggs just until blended (batter will be lumpy). Divide batter evenly among muffin cups (about 2/3 full).
Bake 17 to 21 minutes or until golden brown and tops spring back when touched. Cool 5 minutes; carefully remove from pan (if not using paper cups, run knife around edges of cups before removing). Cool completely before storing.