Just found this thread. It's fascinating, to quote a well known alien.
I think the point of mindfulness is that you are always being mindful. It doesn't mean sitting and contemplating your navel but being awake to all that you are and all that your are doing in that moment.
You mindfully wash the dishes, go for a walk, hang out the washing, hug the children and kiss your spouse. That is you are concentrating only on what you are doing NOW.
Meditation on the other hand is a process where you stop everything and, usually, sit, allowing your mind to empty to connect with what ever divinity/life force/spiritual being/universal karma you believe in or trust.
So while you are mindful of the present moment you cannot be thinking about other horrible stuff or what happened yesterday or will happen tomorrow. Being grateful then becomes the default position.
So without wanting to make this a religious debate, the lilies of the field that "toil not, neither do they spin" that Jesus referred to, are clothed better than Solomon because they, the lilies, were concentrating on their job of growing, not on all the other things they could be doing.
They are being grateful for having soil to grow in and enough rain to drink. Not wanting to have the same shape petals as a daisy, to last as long or have as many flowers. So no John. No need to run through the fields in any way. Just do what comes next and do it by paying attention to what you are doing and how you are doing it. This is why actions such as mindfulness and mediation work. And also work in people with a mental illness.
I see your point about ACT Jess. Seeing that a colleague is talented, watching a great sunset, knowing you have a mental illness and accepting them all without judgement or distress. These things are and go with being mindful about our everyday activities because these are the things we do and must be done to the best of our abilities, like the lilies.