Asking for something, then wanting something else.. tactics?

I have no doubt this is a phase, something they all go through and we just have to work our way through, but here's hoping some one has some good ideas!
Now munchie has developed a brain and some language, she can ask for what she would like to eat. And I let her (to a point) as it's great to see her get excited about food and help mummy pull things out the cupboards now that she recognises what they are.
However, in the last few weeks, she has taken to asking for something, then, a few spoons in, wanting something else and not eating what she asked for.
This morning, breakfast took 1 hour and 10 minutes as I refused to let her have any yoghurt until she had eaten most of her cereals. She'd had about 8 cheerios, then asked for yoghurt and and orange. Great that she is asking for healthy stuff (not that unhealthy foods are on the menu) but, as I have done, if I give her an orange, she'll eat 2 pieces, then want apple...... and so it goes on, until there is a mostly left banquet on her tray
So, what to do? We were supposed to go out this morning, but after the breakfast marathon (and me feeling fairly peed off by the whole thing) we couldn't go. And I had to spoon feed her the cereals that she did have, which took sooooo much coaxing and "no yoghurt until you've had some more...." it's just not what I want to do.
There has to be a balance between happy, fun and bl mealtimes and eating what they've asked for. Isn't there??
Now munchie has developed a brain and some language, she can ask for what she would like to eat. And I let her (to a point) as it's great to see her get excited about food and help mummy pull things out the cupboards now that she recognises what they are.
However, in the last few weeks, she has taken to asking for something, then, a few spoons in, wanting something else and not eating what she asked for.
This morning, breakfast took 1 hour and 10 minutes as I refused to let her have any yoghurt until she had eaten most of her cereals. She'd had about 8 cheerios, then asked for yoghurt and and orange. Great that she is asking for healthy stuff (not that unhealthy foods are on the menu) but, as I have done, if I give her an orange, she'll eat 2 pieces, then want apple...... and so it goes on, until there is a mostly left banquet on her tray

So, what to do? We were supposed to go out this morning, but after the breakfast marathon (and me feeling fairly peed off by the whole thing) we couldn't go. And I had to spoon feed her the cereals that she did have, which took sooooo much coaxing and "no yoghurt until you've had some more...." it's just not what I want to do.
There has to be a balance between happy, fun and bl mealtimes and eating what they've asked for. Isn't there??